During the past seventy years work has been performed on ignition systems for internal combustion engines with the objective of improving the ability of the ignition system to ignite the air-fuel mixture. During the past twenty years much of this work has focussed on improving the ability of ignition systems for igniting very lean mixtures, because such mixtures are inherently cleaner burning, and lead to higher engine operating efficiency.
Most of the work which has been performed falls into two distinct categories: active systems in which there is an actual introduction of additional fuel or chemically active species, such as in the Honda CVCC engine where additional fuel is introduced through an additional valve, or as in continuous (flowing) plasma jets as exemplified by Hilliard and Weinberg, Nature 259 (1976); and passive systems in which there is no actual introduction of additional fuel or chemical species, but rather the creation of new species or new levels of activation by means of spark or other plasma discharges. The predominant and by far simpler type of system is the passive system, the development of a novel type of which is disclosed in this patent application and in my prior U.S. patent application Ser. No. 779,790, now abandoned.
A problem of improving ignition is one of identifying the elements important in ignition and then working to optimize them. There is considerable disagreement on what these elements are. Furthermore, even if they are agreed upon, it is unclear how to create an ignition which both produces these elements and which can then appropriately distribute the energy between or among them. The present invention identifies all the elements and provides a method and system which allows such elements to be excited in an optimal way and a way that can be simply varied to accomodate for differing internal combustion engine environments.
Two of the three elements of ignition are discussed by Taylor Jones "Induction Coil, Theory and Application", Isaac Pitman & Sons, London, 1932, Chapter VIII, "Spark Ignition". Taylor Jones discusses the "Ignition by Capacity and by Inductance Sparks" and shows how the two components can behave differently under different conditions. To quote: "The condenser produces a decided diminution in the igniting power of the spark, and the inferiority of the condenser spark with the spherical electrodes is quite as marked as its superiority when the electrodes are metal points".
In a classic paper "The mechanism of Ignition by Electric Discharges", circa 1935, Bradford and Finch investigate the two phenomena (capacitive and inductive sparks) with reference to the "thermal versus electrical theories of ignition" and again show that the igniting ability of the two componets varies with the circumstance in which they are used. In their discussion they indirectly introduce a third element, namely "excited states". They argue that "the necessary prerequisite for the ignition of an explosive gaseous mixture was the setting up of a sufficient concentration of suitably activated molecules, and . . . ignition by electrical discharge depended on this specific activation and not on the fully degenerate activation associated with thermal energy, as postulated by the thermal theory of ignition." This statement identifying this third factor (intermediate excited states) is at odds with Taylor Jones. Recently, Maly et al, SAE Paper 830478, 1983, "Prospects of Ignition Enhancement" argue that only the capacitive of the three elements is important, while the body of work on plasma jet ignition indicates otherwise.
Generally speaking, the first or capacitive element or component is enhanced by adding a capacitor between the ignition coil high voltage output and ground, as disclosed by all of the above authors, and more recently directly or indirectly by Fitzegerald (U.S. Pat. No. 4,122,816), Ward (U.S. Pat. No. 4,317,068), Anderson and Asik (U.S. Pat. No. 4,487,192), and others. The second or inductive component is enhanced in numerous ways, as in plasma jet ignition (U.S. Pat. Nos. 4,122,816 and 4,317,068 given above), or in more conventional ignitions, such as Ward, U.S. Pat. No. 4,677,960, where a special coil design is used to produce a large inductive component.
The third element and a means to excite it are disclosed in U.S. Pat. Nos. 3,934,566 and 4,138,980, where the concept of electromagnetically stimulated combustion is introduced. The concept here is to maintain a high frequency oscillating electric field of strength of order 1,000 volts/cm/atmosphere at the region of the ignition and flame plasma to excite intermediate molecular levels there. In the above U.S. Pat. No. 4,138,980, Ward discloses means to "ground the spark to the piston face" as well as means "wherein said rf energy is conducted (from an external RF generator) to said chamber through said spark plug".
The present invention discloses that all three elements are important and discloses a system to excite them in conjunction with a large size spark. A preferred system uses a modified form of spark plug--a capacitive plug with an antenna tip--to form a spark to the plug shell and/or piston face and to couple high amplitude electric fields through the spark plug. The fields are generated prior to spark breakdown (and during plug "firing/non-sparking"), and also upon breakdown (spark formation) by converting essentially high voltage DC energy stored in a modified plug to high frequency EM energy which is automatically resonantly stored in the plug and combustion chamber independent of the piston motion (or motion of other opposing movable member, such as the rotor in the Rotary Wankel Engine). The capacitive energy element is preferably stored in the spark plug, while the inductive element is produced by a slight variant of the capacitor and coil combination as disclosed in U.S. Pat. No. 4,677,960, referred to henceforth also as the "CDC ignition" system.